1. Field of the Invention
The present invention relates to a thermal sublimation printer which is used for color printing by transferring sublimating dyes onto paper.
2. Background Art
FIG. 4 is a cross-sectional view showing a thermal transfer in a conventional thermal sublimation printer. In FIG. 4, a paper 1, to which is being transferred sublimating dyes, comprises a base material 1a and an image accepting layer 1b. A donor ribbon 2 comprises a dye layer 2a, an over coat material and a base material 2b. FIG. 5 is a plane view of the donor ribbon 2. In FIG. 5, the dye layer 2a of the donor ribbon 2 is separated into regions 2c coated with yellow dyes, regions 2d coated with magenta dyes, regions 2e coated with cyan dyes, and regions 2f coated with an over coat material. A control unit (not shown) of the thermal sublimation printer and sensor mark 2g are placed on the borders of the over coat material and regions 2c. Furthermore, the control unit (not shown) of the thermal sublimation printer and sensor marks 2h, 2h, . . . , are placed on each border of the regions 2c, 2d, 2e, and 2f.
A platen roller 3 and a thermal head 4 are showed in FIG. 4. A plurality of minute heating elements 4a are built in the thermal head 4. The paper 1 and the donor ribbon 2 contact each other to be pushed by the platen roller 3 and the thermal head 4. The paper 1 moves in the same direction (right or left, as shown) as the rotating direction of the platen roller 3. The donor ribbon 2 moves in direction Y by the action of a rotational axis (not shown). When the heating elements 4a of the thermal head 4 are heated, the dye layer 2a is also heated via the base material 2b of the donor ribbon 2. As a result, dyes of the dye layer 2a, which contact a heated point, melt and diffuse onto the image accepting layer 1b of the paper 1; the dyes then adhere to the surface of the paper 1. For example, when the region 2c of the donor ribbon 2 is placed under the heating elements 4a, yellow dyes adhere to the image accepting layer 1b.
The printing proceeds under the control of the control unit (not shown). In this printing process, while the regions 2c, 2d, and 2e are discriminated by the sensor marks 2g and 2h, the color printing proceeds in the order yellow, magenta, and cyan. Finally, the over coat material is fixed on the paper 1 from the region 2f to protect it from being affected by the atmosphere. The dyes, which are melted and diffused onto the image-accepting layer 1b of the paper 1, are resistant to temperature changes and acid atmospheres.
However, the conventional thermal sublimation printer has some problems. For example, the printer always coats the over coat material on the paper 1, so that wasteful over coating is performed in an area in which over coating is unnecessary. Therefore, the cost of the donor ribbon 2 or the cost of the power for the heating of the thermal head 4 is very high.